Disclosed is a filtration system that utilizes cross flow filtration. More specifically, the present invention relates to an integrated filtration system utilizing ultrasonic assisted cross flow filtration, which system is further integrated with a manufacturing process.
Filtration is a commonly used technique to separate dispersed components from liquids or gases by various separating means such as semi-permeable membranes and other layers or stacks of material containing different perforations. The perforations usually serve to exclude filtered components by size. The most common filtration of dispersed components involves the separation of solids from fluids, and vice versa, through the use of fluid treatment elements, such as filters. Various filtration techniques have been tried in the past, but clogging of filters can be a problem particularly in industrial applications where flow rates are important for process and production rates. Flow rates can diminish upon clogging of the filter through which the fluid passes. Prior art shows different approaches in addressing these problems, either by providing different treatment media, such as polymeric, ceramic or metal filters, or by providing declogging techniques for a given treatment medium, such as electrostatic discharging, heating or ultrasonic agitation.
As described by Haq in U.S. Pat. No. 6,702,941, of the various types of filtration techniques, a type known as “dead-end treatment”, introduces the fluid dispersion to be filtered, or treated, into a fluid treatment element, such as a membrane filter, and the entire amount or substantially all of the fluid passes through the fluid treatment medium of the fluid treatment element to be filtered or otherwise treated. In another type of fluid treatment, known as cross flow filtration, a fluid to be treated is introduced into a fluid treatment element and is made to flow along the surface of a fluid treatment medium of the fluid treatment element. This flow of fluid along the surface is referred to as cross flow. Only a portion of the fluid passes through the fluid treatment medium to be filtered or otherwise treated, while the remainder of the fluid is discharged from the fluid treatment element without passing through the fluid treatment medium. In cross flow filtration, the fluid (feed) stream runs in tangential direction to the filter, such as a membrane filter, for example, establishing a pressure differential across the membrane, causing some of the particles to pass through the membrane. As the remaining particles continue to flow along the membrane, they have the effect of “cleaning it”. The untreated fluid may be recirculated for another pass at the filter element. In contrast to the perpendicular flow of dead-end filtration technique, the use of a tangential flow prevents thicker particles from packing or building up a “filter cake”.
The fluid which is introduced into the element for treatment is referred to as process fluid; the fluid which passes through the fluid treatment medium is referred to as filtrate; and the fluid which is discharged from the fluid treatment element without passing through the fluid treatment medium is referred to as retentate. The cross flow of fluid along the surface of the fluid treatment medium generates a fluid shear force in the fluid adjoining the fluid treatment medium which slows the rate at which particles accumulate on the fluid treatment medium. However, even though cross flow filtration may improve filtration performance in certain applications, the filtration process may further need be augmented by vibrating the filter media or by flow pulsing/reversing for cleaning the filter. Polymers and other chemicals have also been used to reduce caking of solids on the filter media, and additionally, filter-aids like anticoagulant additives have been used to increase flow rates.
Another highly effective technique for enhancing filtration involves ultrasonic cleaning, which is described by Vadoothker in U.S. Pat. No. 6,221,255. Ultrasound is in this arrangement a mechanical form of energy with frequencies above 18 kHz. It can impact solids, liquids, and gasses under appropriate conditions causing either temporary or permanent physical and chemical changes. High frequency (500 kHz) ultrasound waves have been used to bombard aqueous and organic suspensions. This impact breaks the molecules and provides chemically active radicals free to react with other radicals and molecules. Ultrasound has also been well recognized as useful in cleaning applications. As the basis for this serves the ability of ultrasound to vibrate its target to loosen dirt and solids away from the contact surface. Ultrasound applications today abound in medical diagnostics, process control, soldering, and numerous mechanical biological and chemical areas.
The contents of the entire prior art references cited herein are incorporated by reference.
Although ultrasound applications today abound in fields such as diagnostics, process control, soldering and numerous mechanical, biological and chemical areas, the use of sonication needs to be made more adaptable to filtration processes, and hence more practical and cost effective. Usually, when ultrasound transducers are contemplated for use in filtration, they are introduced as an adjunct to the whole process, and therefore are cumbersome. What is needed is a compact and portable filtration system with well integrated ultrasound transducers that, as a whole system, can be made to be more adaptable for use in different applications under different conditions.
For example, certain process sectors on a manufacturing line require special areas delineated from others because of their hazardous nature. These process sectors may also use fluids that require cleaning through filtration. In such situations, the process fluid is normally piped from the hazardous process sector to a separate filtration station outside or adjacent the hazardous sector. Consequently, the various components of a cleaning system, including filters, ultrasonic transducers, pumps and piping required for transferring fluids from the hazardous sector to the filtration station, and vice versa, involve complicated and costly equipment and space. It is desirable, therefore, to be able to bring into such a process sector a compact and portable filtration system that can easily be adapted to be used in that particular process sector on the manufacturing line. Thus, there exists a need for an apparatus or a system that takes advantage of the excellent cleaning properties of ultrasound transducers and integrates them into itself in such a manner so as to improve cleaning process fluids in an efficient and effective way, in particular, in cross flow filtration systems operating in hazardous environments.